Device for signal transmission between moving parts

ABSTRACT

Devices consisting of a signal source and a signal sink connected by a transmission channel for transmitting high-frequency signals, as well as digital signals between moving parts. By eliminating wave reflections, the signals are transmitted such that reliable wide-band transmissions are ensured

[0001] This is a divisional application of U.S. patent application Ser.No. 09/068,884 filed Nov. 9, 1998.

BACKGROUND AND SUMMARY OF THE INVENTION

[0002] The invention relates to devices for transmitting high-frequencyas well as digital signals between moving parts, consisting of a signalsource and a signal sink connected by a transmission channel.Specifically, the present invention relates to the transmission ofhigh-frequency signals such as intermediate-frequency signals or evendigital data, rather than high-performance transmission in the microwaverange. Such signals are normally made available as non-symmetricalsignals.

[0003] High-frequency and also digital signals must frequently betransmitted between parts which are mobile relative to each other. Atypical application of such transmission paths is radar technology,where signals are transmitted from the transmitter/receiver unit to theantenna.

[0004] Various devices are known for transmitting non-symmetricalsignals. For instance, the transmission may be performed in a capacitivemanner via a package of plates resembling a variable capacitor. The mainproblem of this arrangement is the current path between the mutuallymobile parts is not precisely defined.

[0005] Initially, the current flows through the plate package. Thereturn path is normally the frame or chassis, which is mostlyimplemented as a screen or housing. When the parts are rotating relativeto each other, however, it is particularly difficult to achieve aneffective low-inductance frame or ground connection. This results in theinherent problems with the previous transmission systems. In this case,it is very difficult to achieve constant transmission characteristicsand a constant cross-talk.

[0006] Even though transmission paths implemented with the aid ofvariable capacitors have a comparatively large bandwidth, in distinctionfrom other transmission techniques, they present the disadvantage ofhigh engineering expenditures (in terms of the plate packages) and anupper limit frequency which is far below a wavelength corresponding tothe dimensions of the plate package. Another disadvantage of thisarrangement is their high sensitivity to mechanical loads as well asshocks and vibrations.

[0007] Transmission paths based on coupled resonance circuits presentgood transmission characteristics, but naturally they only have a verynarrow band. They have high expenditure requirements (in terms ofmanufacturing technology), and may possibly require trimming. Fordifferent applications, each of these elements must be dimensioneddifferently. As a result, it is nearly impossible to obtain a wide rangeof products with such transmission paths in a standard design.

[0008] In order to avoid the disadvantages of these arrangements,several approaches have been tried to improve the high-frequencytransmission characteristics of conventional collector rings. One suchapproach involves a method of simultaneously inputting the signals atseveral locations so that the occurrence of resonances at elevatedfrequencies is ensured during limited operating conditions. In anotherapproach, attempts have been made to configure a slip ring with adefined wave resistance and to terminate it with the wave resistor at asuitable location.

[0009] Both approaches are entirely unsuitable for broad-bandhigh-frequency transmission because they begin from a closed annularcontact path. This path will always be a capacitive load. Even when aresistor is mounted, which corresponds to the wave resistor, a closedring can never be designed to be free of reflections. With reference toFIG. 4 and FIG. 5, the explanation for this is as follows.

[0010]FIG. 4 shows a closed ring which is designed with a wave resistorof Z_(O)=50 Ω. An impedance 15 with R=50 Ω is mounted on this waveresistor. FIG. 5 shows a small segment of the ring including theimpedance. On the assumption that the ring is actually terminated, andfree of reflections, a wave propagating along the direction wouldencounter an impedance ahead of the impedance 15. This is the result ofmounting in parallel the real resistor (with R=50 Ω) and the line (withZ_(O=)50 Ω) for the purpose of continuing conduction behind theresistor. The value of the parallel circuit is 25 Ω. As a result, theline cannot be free of reflections for the wave ahead of the resistor.Even with all other combinations of wave resistors and terminatingresistors, a line free of reflections is unobtainable.

[0011] The previously described non-contact transmission methods aresuperior to the contacting methods, because they contain a negligibleamount of mechanical friction and hence a lack of abrasion or contactwear. The service life of such non-contact transmission systems isessentially longer than that of the contacting methods. This isparticularly true in the case of high speeds in the relative motion ofthe moving parts. Nevertheless, these transmission methods have theinherent disadvantage of a frequency limit that is lower. As a functionof the particular design, this limit may vary. What is characteristic,however, is the fact that a common-mode component with a frequency of 0(zero) cannot be directly transmitted.

[0012] The digital signals occurring in practical industrialapplication, e.g. the signals used in advanced bus systems, vary betweenalmost static signals with extremely low frequencies and signals with amaximum clock rate predetermined by the bus system. The lowestfrequencies occurring are mostly below the lower limit frequency of thepreviously described non-contact transmission systems.

[0013] Hence a direct transmission of these signals is, as a rule, notpossible. The known modulation or coding methods are a remedy in thisrespect. Both methods require high engineering expenditures. The codingmethods which are well suited for digital signal transmission, such asthe Manchester coding approach, require a wider bandwidth of thetransmission channel merely on account of their coding. As a resultengineering expenditures and costs of the transmission path areincreased. Moreover, regeneration of the digital signal's timing isrequired in the majority of coding applications. This timing isfrequently unreconstructable from the signal. Only with a suitable datastructure, is timing regeneration possible via PLL elements. Suchcircuits are mostly suitable for a previously determined data rate. Inthe event that the non-contact transmission path should be transparentin terms of data and protocol, only the expensive modulation methods canbe employed.

[0014] The object of the present invention is to improve a device fortransmitting signals between mobile elements consisting of a signalsource and a signal sink connected by a transmission channel such that areliable wide-band transmission is ensured. This is accomplished withouta frame or ground connection being required between the moving parts.

[0015] A further object of the present invention is to provide devicesthat are suitable for transmitting high-frequency signals and/or digitalsignals. Moreover, according to the object of the invention, atransmission that is transparent in terms of protocol and data, with adata rate lower than the lower limit frequency of the transmission pathfor the transmission of digital signals should be possible with lowengineering expenditures and without an increased bandwidth requirement.

[0016] These and other objects and advantages are achieved by thepresent invention device, in which a signal source and a signal sink areconnected by a transmission channel such that the transmission path hasa symmetrical structure and hence a precisely defined current path isavailable. The current paths for emission and return are obtained inapproximately identical ways. Therefore, the signal flow must not bereturned via another path which is poorly defined. Hence, poor frame orground connections are irrelevant and a frame or ground connection mayeven be eliminated entirely. As a result, a separation of potentials ofthe parts that are movable relative to each other can be achieved at thesame time. Moreover, due to the symmetrical transmission, an excellentin-phase rejection is achieved. This is particularly expedient, and isspecifically true in those cases which involve poor ground connectionsbetween the moving parts such that substantial differences in voltagemay be present between these elements.

[0017] In one embodiment of the invention, optional matching circuitsare provided for a conversion of non-symmetrical into symmetricalsignals and vice versa. Such matching circuits are necessary when thesignal source, or even the signal sink operate, on non-symmetricalsignals.

[0018] In another embodiment of the invention, the coupler means consistof two oppositely facing pairs of conductive surfaces. The conductorsurfaces should be designed such that they are matched with the path oftravel and the widest possible overlapping of the conductive surfaceswill always be present on the moving parts. The individual conductorsurfaces of each pair should be symmetrical as far as this is possible,in order to ensure the symmetry of the arrangement as a whole.

[0019] In a further embodiment of the invention, the matching circuitsare implemented via passive components. For instance, several circuitsare known for impedance matching and symmetry via lines and also viatransformers are known. Here too, designs using other passive componentsare possible.

[0020] Another embodiment of the arrangement utilizes active componentsin the matching circuits. The functions of these matching circuits canbe implemented by the use of semiconductors and integrated amplifierswithout any additional problems. Moreover, the first matching circuitcan be implemented via an amplifier having an inverting and anon-inverting output. Two separate amplifiers are, of course, equallysuited for application. The second matching circuit can hence beimplemented likewise via a differential amplifier.

[0021] In a yet a further embodiment of the present invention,transmission of digital information, a logic gate with an inverting anda non-inverting output are used in the first matching circuit. Asbefore, two separate logic gates may equally be employed. The secondmatching circuit may be implemented by means of a logic circuit having adifferential input.

[0022] In still another embodiment according to the invention, thebroad-band signal transmission characteristics of a line terminated sothat it is free from reflections is utilized. Such a line may bestructured, in correspondence with the prior art, as a coaxial line, astrip line or as a symmetrical two-wire circuit. Actually, other typesof lines are also suitable for guiding electromagnetic waves. Theelectromagnetic waves have a constant defined wave resistance over theirentire length and are terminated on at least one end with a resistorthat corresponds to the wave resistance such that they are free of fromreflections. The essential aspect, however, is the transmission of TEMwaves on electrical lines.

[0023] As a rule, such lines are terminated on both ends by the waveresistor. However, a signal source with a non-matched internalresistance may equally be connected to a line which, on its part, isterminated with a resistor that corresponds to the wave resistance suchthat it is free of reflections. Reflections cannot occur on thetermination which is free of reflections. With a circular arrangement ofsuch a line, in correspondence with the path of the rotating movement,the information may be obtained along the line.

[0024] In the embodiments reference is made to the term “line”. In fact,this term relates to all lines and also several lines. The term“rotating” movement refers to a rotating motion over any angular rangewhatsoever, and hence even applies to limited angular ranges up tocontinuous rotating movements.

[0025] In a further embodiment of the present invention, the signals are“coupled out” of this line via a high-impedance output circuit. Thishigh-impedance circuit therefore does not give rise to reflections atthe output-coupling site. Such an output circuit may utilize atransformer, or even an amplifier with a high-impedance input or animpedance transformer.

[0026] In another embodiment of the invention, the signal is “coupledout” via a field probe. This probe may be both an E-field probe or anH-field probe. Moreover, the probe can even be a combination of bothtypes and can be a second coupled line. What is essential in the designof the field probe is the fact that it will not influence the field ofthe line in a way which will create reflections on the line. Anattenuation of the signal on the line by the probe is permissible,because any further reflections do not occur in this case.

[0027] In another embodiment of the present invention, signals may evenbe coupled into contact with the line. To this end, it is necessary toterminate the line on both ends in a form that is free of reflections,because waves propagate from the rotatable input site along bothdirections of the line.

[0028] In a further design signals are coupled into the line via acoupler element which achieves the coupling of the E-fields and/or theH-fields. In the simplest form this coupling element may be another linearranged in parallel with the first line.

[0029] In accordance with the object of the invention, the device isconfigured specifically for the transmission of digital signals, suchthat the transmitter is provided with a signal processing circuit whichincreases the slope of the signal flanks of the digital signal suppliedby the data source. This permits the reciprocal values of the rise timeand the drop time to be higher than the lower limit frequency of thetransmission path. Furthermore, a logic evaluation circuit is providedin the receiver which reconstructs the original signals from the pulsessupplied by the transmission path by differentiation of the signalsemitted by the transmitter.

[0030] Other objects, advantages and novel features of the presentinvention will become apparent from the following detailed descriptionof the invention when considered in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031]FIG. 1 is a block diagram illustrating an advantageous embodiment,of the present invention.

[0032]FIG. 2 shows a practical implementation of the coupler means,according to an embodiment of the invention;

[0033]FIG. 3 is a schematic view of an embodiment, according to theinvention;

[0034]FIG. 4 shows a transmission system according to the prior art;

[0035]FIG. 5 is a detail of the illustration in FIG. 4;

[0036]FIG. 6 represents a schematic arrangement of a transmission pathaccording, to an embodiment of the invention;

[0037]FIG. 7 is a schematic view of a transmission path according to theprior art;

[0038]FIG. 8 shows a schematic view of the receiver unit according tothe invention; and

[0039]FIG. 9 is a graph representing the signals generated according tothe present invention in a time/amplitude diagram.

DETAILED DESCRIPTION OF THE DRAWINGS

[0040]FIG. 1 shows an embodiment of the invention, which consists of asignal source 1 and a signal sink 5 connected by the first matchingcircuit 2, the coupler means 3 and the second matching circuit 4.

[0041]FIG. 2 illustrates a practical implementation of the inventivecoupler means. Two conductor surfaces 8 and 9 or 10 and 11,respectively, of approximately the same size are arranged via holdingelements 6 and 7 on the two parts which may be moved relative to eachother. The arrow indicates the principal direction of movement. Withmovements along this direction the quality of transmissions remainsconstant. With movements in all other directions, the quality oftransmissions is subject to very strong variations.

[0042]FIG. 3 illustrates another embodiment of the invention. Here, atransmission path for signal transmission that consists of a transmitterand/or receiver 12, as well as a receiver and/or transmitter 13 forrelative rotation is provided. The transmitter and/or receiver 12 andreceiver and/or transmitter 13 exchange signals via a line 14 which isterminated by an impedance 15 in correspondence with its waveresistance.

[0043]FIG. 4 shows an embodiment that corresponds to the prior art. Itis composed of a transmitter and/or receiver 12 with a line 14 closed toform a ring. The ring is connected to a terminating resistor 15. Thesignals are transmitted to the receiver and/or transmitter 13 inrelative rotation mostly by a galvanic contact with the line 14.

[0044]FIG. 5 serves to explain the impedance situation in an embodimentaccording to FIG. 4 that corresponds to the prior art. On the assumptionthat the line ring is terminated in correspondence with its waveresistance, an electromagnetic wave which propagates along the direction16 meets a parallel-circuit that includes the impedances of the linering 14 and the terminating resistor 15. The total impedance value is,in any case, smaller than the impedance of the line ring and henceprovides for mismatching.

[0045]FIG. 6 depicts one advantageous embodiment of the presentinvention where data is transmitted from the first movable part 56 tothe second stationary part 57. FIG. 6 illustrates a data source 51 and adata sink 55 which are both interconnected via the transmitter/receiver52, the transmission path 53 and the transmitter/receiver 54. Thetransmitter/receiver 52 includes a signal processing circuit 21 thatensures a minimum slope of the signal flanks. An evaluation circuit 41is provided in the transmitter/receiver 54, which reconstructs theoriginal signal from the signal which has been distorted by thetransmission path. Both data source 51 and transmitter/receiver 22 arelocated in first movable part 56, and data sink 55 andtransmitter/receiver 54 are located in second stationary part 57.

[0046] The transmitter 2 is provided with a signal processing circuit21. This circuit increases the flank slope of the digital signalsfurnished by the data source such that the reciprocal values of the riseand decay times are each greater than the lower limit frequency of thetransmission path. The signals processed in this manner are then emittedby the transmitter to the transmission path 3. Because of the band-passcharacteristic of the transmission path, only isolated pulses stillarrive at the receiver 4. The isolated pulses assume positive ornegative values, depending on the flank emitted by the transmitter.

[0047] A signal processing circuit 41 is provided in the receiver 54,which reconstructs the original signal from these pulses. Thereconstructed signal is then transmitted by the receiver 54 to the datasink 55. The evaluation circuit comprises a first comparator fordetecting negative pulses. A digital memory is set by the firstcomparator and reset by a second comparator. As a result, the polarityof the pulse that occurred last is stored. With the pulses occurringonly at signal flanks, they are indicative of variations in the signallevel. As these variations are stored, the output of this memoryreflects the last signal level.

[0048] An evaluation circuit 41 is provided in the receiver, which nowagain reconstructs the original signal from these pulses. The signalreconstructed in this manner is then transmitted by the receiver to thedata sink. In an embodiment of the invention, the evaluation circuitincludes a first comparator for detecting negative pulses. A digitalmemory is set by the first comparator and reset by the secondcomparator. As a result, the polarity of the pulse which occurred lastis stored. With the pulses occurring only at signal flanks, they areindicative of variations in the signal level. As these variations arestored, the output of this memory reflects the last signal level.

[0049]FIG. 7 shows an embodiment that corresponds to the prior art. Itconsists of a data source 61, a transmitter 62, a transmission path 63,a receiver 64, as well as a data sink 65.

[0050]FIG. 8 illustrates a typical structure of the signal processingcircuit 41. This circuit includes a first comparator 42 for detectingpositive pulses, as well as a second comparator 43 for detectingnegative pulses. A digital memory is set by the first comparator 42 andreset by the second comparator 43. Therefore, the polarity of the pulsethat occurred last is stored. The output signals of the first and thesecond comparators are combined with each other via a storage element44. With the pulses occurring only at signal flanks, they are indicativeof variations in the signal level. As these variations are stored, theoutput of this memory reflects the last signal level.

[0051]FIG. 9 explains the mode operation of the embodiment described inFIG. 6. The graph (a) is representative of a typical signal as suppliedby the data source. This signal is not processed by the signalprocessing circuit in the transmitter such that the minimum slope of thesignal flanks will be ensured. This signal is represented by graph (b).Downstream of the transmission path with band-pass characteristics thesignal presents the shape (c). Now the receiver must reconstruct theoriginal signal via an evaluation circuit. When the signal is thenintegrated via an integrator, per an embodiment of the invention, thesignal shape according to graph (d) is obtained. Using anotherembodiment of the invention, the evaluation is performed via twocomparators and a memory. The graph (e) represents the output signal ofthe first comparator for detecting positive pulses, while graph (f)shows the output signal of the second comparator for detecting negativepulses. The output signal of the memory is represented by graph (g).

[0052] The foregoing disclosure has been set forth merely to illustratethe invention and is not intended to be limiting. Since modifications ofthe disclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

16. A device for non-contacting transmission of signals between movingparts, comprising: a data source for generating the signals; atransmitter for transmitting the signals to the receiver via anon-contacting transmission path, the transmission path having aband-pass characteristic; and a data sink for receiving data from thereceiver; said transmitter further having a signal processing circuitfor increasing the slope of a leading and trailing edge of the signalgenerated by the data source such that reciprocal values of a rise anddecay time of the signal are higher than a lower limit frequency of thetransmission path; wherein an evaluation circuit in said receiverreconstructs the signals from pulses received from said transmissionpath generated by a differentiation of the signals emitted by saidtransmitter.
 17. The device according to claim 16, evaluation circuitfurther comprises: an integrator for integrating pulses arriving fromsaid transmission path and outputting the integrated signal to said datasink.
 18. The device according to claim 16, evaluation circuit furthercomprises: a first comparator for detecting positive pulses and a secondcomparator for detecting negative pulses; and a memory element connectedto said first and second comparator for storing polarity of the pulsewhich occurred last, using the output signals of said comparators;wherein the memory element outputs a signal to said data sink thatcorresponds to a stored condition.
 19. The device according to claim 17,wherein said evaluation circuit further comprises: a first comparatorfor detecting positive pulses and a second comparator for detectingnegative pulses; and a memory element connected to said first and secondcomparator for storing polarity of the pulse which occurred last, usingthe output signals of said comparators; wherein the memory elementoutputs a signal to said data sink that corresponds to a storedcondition.
 20. The device according to claim 16, wherein the transmittedsignals are digital signals.
 21. The device according to claim 17,wherein the transmitted signals are digital signals.
 22. A method ofdevice of transmitting signals between non-contacting moving parts,comprising the steps of: generating the signals using a data source;transmitting the signals to the receiver via a non-contactingtransmission path with a transmitter having a signal processing circuitfor increasing the slope of a leading and trailing edge of the signalgenerated by the data source such that reciprocal values of a rise anddecay time of the signal are higher than a lower limit frequency of thetransmission path; receiving data from the receiver with a data sink;and wherein an evaluation circuit in said receiver reconstructs thesignals from pulses received from said transmission path generated by adifferentiation of the signals emitted by said transmitter.
 23. Themethod according to claim 22, the method further comprising the step of:integrating pulses arriving from said transmission path and outputtingan integrated signal to said data sink with an integrator.
 24. Themethod according to claim 22, the method further comprising the stepsof: detecting positive pulses with a first comparator and a negativepulses with a second comparator; and storing the polarity of the pulsewhich occurred last, using the output signals of said comparators in amemory element connected to said first and second comparator; outputs asignal to said data sink that corresponds to a stored condition with thememory element.
 25. The method according to claim 23, the method furthercomprising the steps of: detecting positive pulses with a firstcomparator and a negative pulses with a second comparator; and storingthe polarity of the pulse which occurred last, using the output signalsof said comparators in a memory element connected to said first andsecond comparator; outputs a signal to said data sink that correspondsto a stored condition with the memory element.
 26. The method accordingto claim 22, wherein the transmitted signals are digital signals. 27.The method according to claim 22, wherein the transmitted signals aredigital signals.